초록 ▼

A roller cutter (28) for a rotary drill bit (10) and method of making, utilizing an ion nitriding hardening process for the external surface (42) and the internal bearing surfaces (33, 34, 38) in the central cavity (30) of the roller cutter (28). The roller cutter (28) is made from a through hardena

A roller cutter (28) for a rotary drill bit (10) and method of making, utilizing an ion nitriding hardening process for the external surface (42) and the internal bearing surfaces (33, 34, 38) in the central cavity (30) of the roller cutter (28). The roller cutter (28) is made from a through hardenable steel and the ion nitrided hardened layer (77) has a total thickness less than around 0.030 inch. Hardened layer (77) has a relatively thick inner stratum (80) and a relatively thin outer surface stratum (78). The outer stratum (78) is formed of Fe4N having a thickness no greater than around 0.0004 inch to form an outer surface which is ductile and has a relatively low friction coefficient.

대표청구항 ▼

A method of making a generally conical-shaped roller cutter for a rotary drill bit from a through hardening steel comprising the steps of: forming a roller cutter body from the through hardening steel, the body including a generally conical external surface and a central cavity forming internal fric

A method of making a generally conical-shaped roller cutter for a rotary drill bit from a through hardening steel comprising the steps of: forming a roller cutter body from the through hardening steel, the body including a generally conical external surface and a central cavity forming internal friction bearing surfaces for fitting against a journal of the drill bit; heat treating said roller cutter body to obtain a yield strength of at least around 150,000 psi; placing the roller cutter body in a low pressure vessel containing a mixture of nitrogen and hydrogen gases; heating the roller cutter body in a low pressure vessel containing a mixture of nitrogen and hydrogen gases; heating the roller cutter body in the vessel to a temperature of at least around 750°F.; applying high voltage DC power between the vessel and the roller cutter body with the vessel acting as an anode and the roller cutter body acting as a cathode to provide a glow discharge to effect ionizing of nitrogen and the sputtering of nitrogen ions against friction bearing surfaces defined within the central cavity of the roller cutter body thereby to penetrate and harden said internal friction bearing surfaces; and maintaining said roller cutter body in said vessel at said temperature for a predetermined period of time sufficient to provide an ion nitrided hardened layer for said friction bearing surfaces of at least around 0.005 inch in thickness with a minimum hardness of at least RC50, said yield strength of said roller cutter body being maintained at a minimum of around 150,000 psi after providing said ion nitrided hardened layer.